Patent GB-628425-A (GB)
Title: Improvements in or relating to electric time modulation systems of communication
IPC: H04J3/04
Filed: 1947-09-12
Abstract: 628,425. Multiplex pulse signalling ; pulse delaying circuits. STANDARD TELEPHONES & CABLES, Ltd., and KRAMSKOY, C. M. Sept. 12, 1947, No. 25064. [Classes 40 (v) and 40 (vi)] In a multiplex communication system using interlaced time modulated pulse trains, a pair of modulating or demodulating trigger devices is provided, which operate alternately, a distributer being used to apply the channel signal circuits in turn alternately to said devices. In the transmitting system described, a master pulse generator 1, Fig. 1, having a pulse recurrence frequency of 9 kc/s., and a pulse shaping network 2 feed a pulse distributee. 3 sending interlaced trains of ten microsecond pulses to thirteen channel output terminals 7. The generator 1 also feeds a pulse shaping network 5, through a delay network 4, to produce suitably timed two micro, second synchronizing impulses which are fed to the output mixer 6. The pulses from distributor 3 are spaced apart by eight microseconds and are fed through six microsecond delay networks 8 to gate channel signal amplifiers 9, those for odd numbered channels feeding modulator 11 and those for even channels feeding modulator 12. The modulators are also fed with short negative triggering pulses derived from the distributer terminals 7 by differentiating circuits 13 and rectifiers 14, modulator 11 being fed with those from the odd numbered outputs and modulator 12 with those from the even ones. The time modulated half microsecond channel pulses from the modulators are mixed with the synchronizing pulses in output mixer 6. A suitable modulator circuit comprises pentodes 21, 22, Fig. 3, to which are fed the paralleled outputs of the channel signal amplifiers 50. The signals are applied to the control grids of valves 50 from terminals 10 and the gating pulses to their suppressor grids from delay networks 8. A trigger pulse is applied through condenser 49 to the anode circuit of valve 21, which is normally non-conducting, and suddenly reduces its anode potential. This drop is fed through condenser 40 to the control grids of valves 21 and 22, to cut-off the normally conducting valve 22. The anode potential of valve 22 rises and raises the suppressor grid potential of valve 21 through circuit 41, 42, 43 to restore anode current to this valve. The reduction of anode voltage is fed to the control grid and to the cathode which follows the grid the effect being cumulative. When the screen current begins to increase, a point is reached when the anode potential remains stationary and the control grid potential then rises sharply to unblock the valve. At this point, the suppressor grid potential falls to the negative value determined by terminal 25 and the anode voltage rises until limited to the maximum value determined by the potential, determined by the appropriate signal and then present at the anodes of valves 50 which is operative through diode 54. The time taken for the anode voltage of valve 21 to reach its lowest value depends on the initial value of this potential, so that the duration of the pulse generated at the control grid of valve 22 also depends on this potential. This pulse is differentiated by circuit 45, 46 to produce a time modulated pulse selected by rectifier 47 and passed to the output terminal 48 leading to mixer 6. At the receiver, Fig. 4 (not shown), two demodulators feed output amplifiers, for the odd and even numbered channels respectively, which are gated by pulses derived from the received synchronizing pulses. The signal pulses are all fed to both demodulators which are also fed with triggering pulses derived from the synchronizing pulses through a distributer. The demodulators produce duration modulated pulses, whose leading edge coincides with the triggering pulse and whose trailing edge coincides with the associated channel pulse. The demodulator circuit, Fig. 5 (not shown), is similar to the modulator circuit, Fig. 3.